The present invention is a response to the problem of establishing high purity tantalum wire with under 100 ppm of oxygen impurity for use as an effective lead wire for sintered tantalum powder solid electrolytic capacitors. The invention also involves other metals and usage of such other metals and tantalum in applications other than as lead wires.
In working with tantalum and other reactive metals used for lead wires, and in similar application, problems arise out of the affinity of such metals to oxygen and the high temperatures normally associated with extrusion, forging and other fabrication of such metals. It is known that oxygen contents of several hundred ppm typically encountered with sodium reduced tantalum (i.e, reduction of K.sub.2 TaF.sub.7 or other salts of tantalum by sodium) will lead to difficulties in later working. The high temperatures of extrusion and/or encountered in the course of anneals and other softening treatments in the course of cold fabrication processes complicate the problem. See, e.g., Michaluk et al., "Characterization of Extruded and Forged Preforms," 1992 paper for a book published that year by the Mineral, Metals and Materials Society.
It is the object of this invention to provide new and improved processing of tantalum and other reactive metals.